The present invention relates to a planar optical waveguide.
An optical waveguide is an important component in the field of telecommunication. A special type of optical waveguide is a planar optical waveguide, which can be manufactured as a part of an integrated circuit.
Nowadays, optical signals are very important for transmitting information. However, when an optical signal is transmitted through an optical fiber, attenuation will always occur to a certain extent, such that it is necessary to amplify the signal after a certain distance (typically in the order of about 50-100 km). Conventionally, for that purpose an electronic amplifier is used. At the amplifier station, the optical signal must then be converted into an electrical signal, which is amplified in an electronic amplifer, after which the amplified electrical signal is converted back into an optical signal. This involves not only the disadvantage that an amplifier station has a rather complicated structure with rather a large number of parts, among which optical/electrical converters and electrical/optical converters, but this also implies that the bandwith and bit-rate of the overall system is limited by the electronical components.
Therefore, optical fibre amplifiers have recently been developed, i.e. amplifiers which amplify the optical signal directly and do not need a conversion into an electrical signal.
Similarly, integrated planar waveguide amplifiers are of necessity in order to realize all-optical telecommunication. For example, a planar waveguide amplifier can be integrated with a passive splitter as loss-compensating components. Due to their small sizes, planar optical waveguide amplifiers are expected to be of low cost, and more importantly, they offer the promise of integrating passive and active functions on the same substrate.
Materials for planar optical waveguides can be divided into different categories, among which:
(1) crystalline materials (LiNbO.sub.3, Al.sub.2 O.sub.3, Y.sub.2 O.sub.3, etc.) PA1 (2) glassy materials, such as silicate-glass (based on SiO.sub.2), phosphate-glass (based on P.sub.2 O.sub.5), etc.